1. Technical Field
This invention relates to systems and methods for the quantitation of whole body distribution of radiopharmaceuticals in nuclear medicine, and in particular to a system for determining the percentage uptake of a radiopharmaceutical in a selected region of the body.
2. Discussion
The field of nuclear medicine has developed imaging techniques which make it possible to examine functions of the human body non-invasively. This has resulted in great advances in medical diagnosis, treatment, and research. In nuclear medicine, the body is viewed as a complex array of coordinated and physical motions, making possible a new approach to disease and providing the ability to recognize disease at a much earlier functional stage, even before detectable structural changes have occurred. One example is bone imaging, which can detect some focal diseases even before microscopic changes can be detected.
In a typical nuclear imaging examination, a tracer comprised of a radioactive isotope is given, usually by injection into an arm vein, and the distribution of the radioactive substance within the body or a part of the body is portrayed in a series of nuclear images. These images, which result from the emission of gamma rays by the tracer substance passing out of the body, are recorded by a scintillation camera. A scintillation camera is a radiation detection device, typically consisting of a large sodium iodide crystal which detects the gamma rays that interact with the crystal by detecting the photons produced in this interaction. In this way, the scintillation camera locates where on the detector face the interaction occurred. These interactions are used to produce a picture, or image, of where the gamma rays originated within the body. These images are similar to those in routine x-ray examinations, except that gamma rays are emitted from the body to provide the diagnostic information, rather than being transmitted through the body. Nuclear images depend on specific radioactive elements or compounds labeled with radioactive elements being selectively concentrated in an organ, making it possible to obtain pictures that provide information about regional function within the organ.
In many nuclear imaging techniques, besides the information gained from viewing the resulting image, it is frequently desirable to quantify the amount of the radio-pharmaceutical which has been absorbed in a particular region of the body. For example, by knowing the total amount of gamma rays emitted from the body (as measured by the number of counts detected by the scintillation camera over the whole body) and by knowing the total number of counts emitted by one portion of the body such as the kidney, the percentage uptake of the radio-pharmaceutical by the kidney can be determined. This percentage can then be used in diagnosis, or in therapy. In diagnosis, the percentage uptake by the kidney may be compared with the percentage expected from a normal kidney. In therapy, the percentage uptake by the kidney can be used to determine how much of a total isotope will be taken up by a cancerous kidney, for example, in the treatment of this cancer. Prior techniques for quantitation of organ activity as a percentage of whole body activity generally use techniques which analyze individual anterior and posterior images of the body using conventional region of interest (ROI) techniques. Unfortunately, these techniques are time consuming and potentially inaccurate, particularly for organs that are well visualized in only one view. This is because the lack of visual information hampers the ability to accurately place the ROI. Accordingly, it would be desirable to provide a technique for quantitation of organ activity as a percentage of whole body activity of a radiopharmaceutical that is relatively fast and which produces accurate results. Further, it would be desirable to provide such a system which produces accurate results even for organs that are well visualized in only one view.